U.S. patent application number 15/918093 was filed with the patent office on 2019-09-12 for low reflectivity lcd with cop retarder and cop matching rm.
The applicant listed for this patent is Sharp Kabushiki Kaisha. Invention is credited to Andrew Acreman, Hywel Hopkin, Yuichi Kawahira, Kiyoshi Minoura, Koji Murata, Akira Sakai, Nathan James Smith, Jiyun Yu.
Application Number | 20190278120 15/918093 |
Document ID | / |
Family ID | 67844538 |
Filed Date | 2019-09-12 |
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United States Patent
Application |
20190278120 |
Kind Code |
A1 |
Smith; Nathan James ; et
al. |
September 12, 2019 |
LOW REFLECTIVITY LCD WITH COP RETARDER AND COP MATCHING RM
Abstract
A liquid crystal device (LCD) is configured for minimizing
unwanted internal ambient light reflections. The LCD includes a
plurality of layers, the layers comprising from a viewing side: a
first linear polariser; an external retarder that is made of a
cyclic olefin polymer (COP) material or a cyclic olefin copolymer
(COC) material; a colour filter substrate; a colour filter layer;
an internal reactive mesogen (RM) retarder alignment layer; an
internal reactive mesogen (RM) retarder; a liquid crystal (LC)
layer; and a second linear polarizer. The external retarder and the
internal RM retarder are configured such that the optical
properties (for example light polarization control function) of the
external retarder and the internal retarder are matched to negate
each other for light passing through the external retarder and the
internal RM retarder. The LCD simultaneously maintains high image
quality in both high and low ambient lighting conditions.
Inventors: |
Smith; Nathan James;
(Oxford, GB) ; Acreman; Andrew; (Oxford, GB)
; Hopkin; Hywel; (Oxford, GB) ; Minoura;
Kiyoshi; (Osaka, JP) ; Murata; Koji; (Osaka,
JP) ; Kawahira; Yuichi; (Osaka, JP) ; Sakai;
Akira; (Osaka, JP) ; Yu; Jiyun; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sharp Kabushiki Kaisha |
Osaka |
|
JP |
|
|
Family ID: |
67844538 |
Appl. No.: |
15/918093 |
Filed: |
March 12, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 1/13394 20130101;
C09K 2323/00 20200801; G02F 2001/133565 20130101; G02F 2413/11
20130101; G02F 2001/133726 20130101; C09K 2323/03 20200801; G02F
2413/06 20130101; G02F 1/133514 20130101; G02F 1/13363 20130101;
G02F 2001/133334 20130101; G02F 1/133528 20130101; G02F 2413/02
20130101; G02F 1/133711 20130101; G02F 2001/133633 20130101; G02F
1/133634 20130101; G02F 2001/133638 20130101; G02F 2001/133531
20130101; G02F 2001/133357 20130101 |
International
Class: |
G02F 1/13363 20060101
G02F001/13363; G02F 1/1335 20060101 G02F001/1335; G02F 1/1337
20060101 G02F001/1337; G02F 1/1339 20060101 G02F001/1339 |
Claims
1. A liquid crystal device (LCD) comprising a plurality of layers,
the layers comprising from a viewing side: a first linear
polariser; an external retarder that is made of a cyclic olefin
polymer (COP) material or a cyclic olefin copolymer (COC) material;
a colour filter substrate; a colour filter layer; an internal
reactive mesogen (RM) retarder alignment layer; an internal
reactive mesogen (RM) retarder; a liquid crystal (LC) layer; and a
second linear polarizer.
2. The LCD of claim 1, wherein the external retarder and the
internal RM retarder are configured such that optical properties of
the external retarder and the internal RM retarder are matched to
negate each other for light passing through the external retarder
and the internal RM retarder.
3. The LCD of claim 2, wherein the matched optical properties
include light polarization control function.
4. The LCD of claim 1, wherein an azimuthal angle between the first
and second linear polarisers is 90.degree., an azimuthal angle
between the first linear polariser and the external retarder is
45.degree., and an azimuthal angle between the internal RM retarder
and external retarder is 90.degree..
5. The LCD of claim 1, wherein the internal RM retarder is made of
a positive uniaxial material.
6. The LCD of claim 1, wherein the external retarder is made of a
positive uniaxial material.
7. The LCD of claim 1, wherein the external retarder is a laminated
film that is configured as a quarter wave plate.
8. The LCD of claim 1, wherein the internal RM retarder is a film
that is configured as a quarter wave plate.
9. The LCD of claim 1, wherein the internal RM retarder and the
external retarder layer each has a retardation value in a range of
110 nm to 165 nm measured at 550 nm.
10. The LCD of claim 9, wherein a difference in retardation values
measured at 550 nm between the internal RM retarder layer and the
external retarder layer is in a range of 0 nm to 10 nm.
11. The LCD of claim 1, wherein: R450 denotes retardation of blue
light measured at 450 nm, R550 denotes retardation of green light
measured at 550 nm, and R650 denotes retardation of red light at
650 nm; and the internal RM retarder layer has a value of R450/R550
in a range of 0.95 to 1.07 (1.01.+-.0.06), and a value of R650/R550
in a range of 0.93 to 1.05 (0.99.+-.0.06).
12. The LCD of claim 1, wherein: R450 denotes retardation of blue
light measured at 450 nm, R550 denotes retardation of green light
measured at 550 nm, and R650 denotes retardation of red light at
650 nm; and the external retarder has a value of R450/R550 in a
range of 0.95 to 1.07 (1.01.+-.0.06), and a value of R650/R550 in
the range of 0.93 to 1.05 (0.99.+-.0.06).
13. The LCD of claim 1, further comprising an electromagnetic
shielding layer that is deposited onto the color filter substrate
and is positioned between the colour filter substrate and the
colour filter layer.
14. The LCD of claim 13, wherein the electromagnetic shielding
layer is a conductive layer.
15. The LCD of claim 1, further comprising a first planarization
layer deposited on a non-viewing side of the colour filter layer
that eliminates surface roughness of the colour filter layer.
16. The LCD of claim 15, further comprising a second planarization
layer deposited on the non-viewing side of the internal RM retarder
that eliminates surface roughness of the internal RM retarder.
17. The LCD of claim 1, further comprising a photospacer layer
deposited on a non-viewing side of the internal RM retarder that is
configured to maintain uniform thickness of the LC layer.
18. The LCD of claim 1, further comprising an anti-reflection film
located on the viewing side of the first linear polarizer.
19. The LCD of claim 1, further comprising at least one C-plate
retarder deposited between the external retarder and internal RM
retarder.
Description
TECHNICAL FIELD
[0001] The present invention has application within the field of
displays which are particularly suitable for outdoor use and other
comparable potentially high ambient illumination situations.
BACKGROUND ART
[0002] In recent years, the performance of transmissive or emissive
type displays, such as liquid crystal displays (LCDs) and organic
light-emitting diode displays (OLEDs), has increased significantly
in metrics such as resolution, colour gamut capability and
brightness. Such displays also have decreased in cost such that
they now form the large majority of the electronic displays market
for most applications, both static and mobile, indoor and outdoor
use. This has resulted in the retreat of reflective and
transflective display types into niche applications for very high
ambient illumination applications, and long battery life
requirement applications.
[0003] Even applications which until very recently a reflective
display technology was preferred, such as outdoor signage,
e-readers and smart wristwatches, and similar devices commonly used
outdoors, are now largely being served by transmissive or emissive
devices, due to their increased image quality capability. In these
areas, and others in which a display device may be intended for use
mainly in moderate ambient light, or only occasionally high ambient
light situations, such as smartphones, tablets, automotive displays
and notebook PCs, attempts have been made to modify transmissive or
emissive type displays to have improved performance in higher
ambient lighting situations, with minimal impact on cost and dark
room performance. Such modifications include the use of
anti-reflection or anti-glare films to reduce reflections from the
front surface of the display, and a circular front polariser to
absorb reflection of ambient light from within the display.
Circular polarisers are particularly effective at removing internal
reflections, and as a result are used in displays such as LCDs in
which higher dark room contrast may be obtained using standard
linear polarisers (also sometimes referred to as plane polarizers),
and OLEDs which do not use polarised light and therefore an emitted
brightness loss is incurred.
[0004] The dominant LCD display technology for high resolution,
narrow-bezel, wide-viewing angle applications, such as smartphones
and tablets, utilizes a Fringe-Field Switching (FFS) mode. The FFS
mode is not conventionally compatible with circular polarisers, as
at all voltage conditions, including zero, they have an LC director
orientation, and therefore optic axis, with a large component in
the polarisation plane of on-axis light, so no black state is
achievable. This is also true for other commonly used LC modes such
as In-Plane Switching (IPS), Twisted Nematic (TN) and Electrically
Controlled Birefringence (ECB). These LC modes rely on the use of
linear polarisers having a transmissive axis aligned parallel or
orthogonal to the projection of the optical axis of the LC in the
plane of the cell, in at least one of the display voltage states to
produce a particular transmission condition.
[0005] US 2010/0134448 (Park et al., published Jun. 3, 2010)
describes the use of phase compensation (retarder) films integrated
into a touch panel to improve the outdoor visibility and viewing
angle characteristics of an LCD. JP 2008-83492 (Epson Imagining
Devices Co., Ltd) describes the use of phase compensation
(retarder) films for preventing deterioration in display quality
due to static electricity and reflected light. US 2017/0031206
(Smith et al., published Feb. 2, 2017) and commonly assigned
PCT/JP2016/003507 describe the use of phase compensation (retarder)
films for preventing deterioration in display quality due to
reflected light.
SUMMARY OF INVENTION
[0006] It is desirable to provide an LC display in which an LC mode
configuration typically used in conjunction with linear polarisers
for optimum low ambient light image quality is utilized with a
circular front polariser to improve high ambient lighting
appearance, via absorption of the uncontrolled ambient light
reflection from internal display components, while retaining the
high quality transmissive display performance associated with the
LC mode. While light transmitted by the display from the backlight
to the viewer is modulated by the LC layer as expected to give the
intended transmission, in conventional configurations unwanted
ambient light reflected from internal layer interfaces is
re-emitted (reflected) without control in all LC states, resulting
in reduced contrast ratio for the display and degraded image
quality.
[0007] The present disclosure relates to display configurations
that reduce ambient light reflections in liquid crystal devices
(e.g., displays and light modulators), and, more particularly from
IPS or FFS type displays so as to provide enhanced contrast ratio
and image quality particularly in conditions of high ambient light.
More generally, this disclosure relates to reducing ambient light
reflections in liquid crystal devices such as displays and light
modulators that are normally operated with at least a first linear
polariser and often with a second linear polariser, such as FFS,
IPS, VAN, TN modes and the like. Accordingly, ambient light
reflections are reduced in liquid crystal devices that are not
normally used with circular polarisers.
[0008] In embodiments described in this disclosure, enhanced
contrast ratio and overall performance are achieved via (i) the
addition of at least one uniform, unpatterned retarder layer on an
inner surface of the LC cell and (ii) the use of a circular
polariser, comprised of an external retarder layer and a linear
polariser, on an outside surface of the LC cell. The external
retarder and the internal retarder effectively cancel as completely
as possible each other's polarisation control function for all
wavelengths transmitted by the LCD, thus ensuring high contrast
ratio for images viewed in dark room (low ambient lighting)
conditions. The circular polariser significantly reduces unwanted
ambient reflections from inner surfaces of the LC cell, thus
ensuring high contrast ratio for images viewed in high ambient
lighting conditions. It is well known that LCDs that are
conventionally operated with two linear polarisers (no circular
polarisers), such as FFS, IPS, TN and like display technologies,
have lower contrast ratio for images viewed in high ambient
lighting conditions than for images viewed under the same ambient
lighting conditions on LCDs that are conventionally operated with
two circular polarisers. However, it is not possible to simply
replace the linear polarisers for circular polarisers in displays
such as FFS, IPS, and TN displays without significantly degrading
the image quality. Aspects of the current invention demonstrate how
additional optical layers, such as an internal retarder and an
external retarder, may be added to an LCD that is conventionally
operated with two linear polarisers to enable the viewing of high
contrast ratio images in both low and high ambient lighting
conditions.
[0009] The present invention results in an LC display configured
for optimum low ambient light image quality and improved high
ambient lighting appearance, via absorption of the uncontrolled
ambient light reflection from internal display components, while
retaining the high quality transmissive display performance
associated with the LC mode. Ambient light reflections in liquid
crystal displays are thereby by reduced, and more particularly from
IPS or FFS type displays, so as to provide enhanced contrast ratio
and image quality.
[0010] An aspect of the invention, therefore, is a liquid crystal
device (LCD) that is configured for minimizing unwanted ambient
light reflections particularly from internal components. In
exemplary embodiments, the LCD includes a plurality of layers, the
layers comprising from a viewing side: a first linear polariser; an
external retarder that is made of a cyclic olefin polymer (COP)
material or a cyclic olefin copolymer (COC) material; a colour
filter substrate; a colour filter layer; an internal reactive
mesogen (RM) retarder alignment layer; an internal reactive mesogen
(RM) retarder; a liquid crystal (LC) layer; and a second linear
polarizer. The external retarder and the internal RM retarder are
configured such that optical properties (for example light
polarization control function) of the external retarder and the
internal retarder are matched to negate each other for light
passing through the external retarder and the internal RM retarder,
thereby minimizing said unwanted internal ambient light
reflections. An azimuthal angle between the first and second linear
polarisers may be 90.degree., an azimuthal angle between the first
linear polariser and the external retarder may be 45.degree., and
an azimuthal angle between the internal RM retarder and external
retarder may be 90.degree..
[0011] In exemplary embodiments, the internal RM retarder and the
external retarder layer each has a retardation value in a range of
110 nm to 165 nm measured at 550 nm, and a difference in
retardation values measured at 550 nm between the internal RM
retarder layer and the external retarder layer is 0 nm to 10 nm. As
used herein, R450 denotes retardation of blue light measured at 450
nm, R550 denotes retardation of green light measured at 550 nm, and
R650 denotes retardation of red light at 650 nm. In exemplary
embodiments, the internal RM retarder layer has a value of
R450/R550 in a range of 0.95 to 1.07 (1.01.+-.0.06), and a value of
R650/R550 in a range of 0.93 to 1.05 (0.99.+-.0.06).
[0012] To the accomplishment of the foregoing and related ends, the
invention, then, comprises the features hereinafter fully described
and particularly pointed out in the claims. The following
description and the annexed drawings set forth in detail certain
illustrative embodiments of the invention. These embodiments are
indicative, however, of but a few of the various ways in which the
principles of the invention may be employed. Other objects,
advantages and novel features of the invention will become apparent
from the following detailed description of the invention when
considered in conjunction with the drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a schematic drawing of an optical stack
arrangement of an LCD as is conventional in the art.
[0014] FIG. 2 is a schematic drawing of an exemplary LCD optical
stack arrangement in accordance with embodiments of the present
invention.
[0015] FIG. 3 is a drawing that defines the azimuthal orientation
directions of the LCD in accordance with embodiments of the present
invention.
[0016] FIG. 4 is a chart that defines the azimuthal orientation
directions of some optical components pertaining to the LCD shown
in FIG. 2.
[0017] FIG. 5 is a schematic drawing of another LCD optical stack
arrangement in accordance with embodiments of the present
invention.
[0018] FIG. 6 is a schematic drawing of another LCD optical stack
arrangement in accordance with embodiments of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0019] For comparison purposes for illustrating the enhancements of
the present invention, FIG. 1 is a schematic drawing of an optical
stack arrangement of an LCD as is conventional in the art.
Referring to FIG. 1, a transmissive FFS or IPS type LCD 100 of a
conventional configuration, which may be considered standard in the
art, typically comprises an optical stack configuration in which
the liquid crystal (LC) material 5 is sandwiched between a TFT
substrate 2 and colour filter (CF) substrate 10 with a uniform cell
gap of typically 3-5 .mu.m. First and second LC alignment layers 4
and 6 are disposed on the inner surfaces of the TFT substrate and
CF substrate adjacent to the LC material to promote a uniform,
antiparallel planar alignment of the LC. A colour filter (CF) layer
9 is disposed on the colour filter substrate 10, and an
active-matrix pixel array and drive electronics 3 are disposed on
the inner surface of the thin film transistor (TFT) substrate 2.
Linear polarisers 1 and 12 are laminated onto the outer surfaces of
both the TFT substrate and CF substrate, resulting in the
transmission of linearly polarised light into the display stack
from both the backlight 300 and from ambient illumination on the
viewing side 200.
[0020] The viewing side sometimes is referred to as the viewer side
or the outer side of the LCD, and is the side at which a person
typically would look at or view images on the LCD, from which
images may be provided for projection, and so on. Relative to the
illustrations in the drawings, the top, upper or outer side of the
LCD or of an element, component or layer of the LCD is at the top
of the respective illustrations, e.g., is closer to the viewing
side than to the other side of the LCD, which commonly is referred
to as the non-viewing side, bottom, lower, inner, or back side, or
in some cases the backlight-side of the LCD. In some instances the
term "inner surface" may represent a surface that is inside the
stack of components or layers of the LCD, e.g., between the
respective TFT substrate 2 and CF substrate 10 of the LCD, as will
be evident from the description with reference to the illustrations
in the respective drawings. The term "external" generally refers to
a location not between the TFT substrate 3 and CF substrate 10. The
term "internal" generally refers to a location between the TFT
substrate 2 and CF substrate 10.
[0021] A disadvantage of the transmissive FFS or IPS type LCD 100
shown in FIG. 1 is that a portion of the ambient lighting (such as
sunshine etc.) incident upon the FFS or IPS type LCD 100 from the
viewing side 200 is reflected back to the viewer. This unwanted
reflected light degrades the perceived image quality of the FFS or
IPS type LCD 100. In particular, the reflected light degrades the
perceived contrast ratio of the FFS or IPS type LCD 100. A first
portion of unwanted reflected ambient light comes from the
upper-most layer on the viewing side and is referred to as external
reflections as these unwanted reflections occur external to the
image forming components of the FFS or IPS type LCD 100. In other
words, external reflections have occurred from components not
situated between the TFT substrate 2 and the CF substrate 10. This
first portion of light reflected from FFS or IPS type LCD 100 can
be reduced by use of an anti-reflection film 13 that is deposited
on the viewing side of the first linear polarizer 12, and typically
is the upper-most layer closest to the viewing side of the FFS or
IPS type LCD 100.
[0022] A second portion of unwanted reflected ambient light comes
from the materials and interfaces used within the transmissive FFS
or IPS type LCD 100, and these unwanted reflections are therefore
referred to as internal reflections. In other words, internal
reflections have occurred from components situated between the TFT
substrate 2 and the CF substrate 10. The total portion of unwanted
reflected light is the sum of the first portion (unwanted external
reflections) and second portion (unwanted internal reflections).
Although a high quality anti-reflection film can significantly
suppress unwanted external reflections, the unwanted internal
reflections must be reduced to maintain high image quality of the
FFS or IPS type LCD 100.
[0023] Configurations intended for suppressing the unwanted
internal reflections have been attempted. For example, suppression
of unwanted internal reflections via the use of an internal optical
retarder film and an external optical retarder film has been
previously disclosed (see US 2017/0031206, cited in the background
section above). In exemplary embodiments of the present invention,
optimum materials and processing conditions for the external
retarder and internal retarder are disclosed as inventive
improvements over such previous configuration. Further in exemplary
embodiments of the present invention, optimum orientations for the
external and internal retarders in relation to other optical
components of an FFS or IPS type LCD are disclosed. Further in
exemplary embodiments of the present invention, additional
components of an FFS or IPS type LCD are disclosed for improved
display performance.
[0024] An aspect of the invention, therefore, is a liquid crystal
device (LCD) that is configured for minimizing unwanted ambient
light reflections particularly from internal components. In
exemplary embodiments, the LCD includes a plurality of layers, the
layers comprising from a viewing side: a first linear polariser; an
external retarder that is made of a cyclic olefin polymer (COP)
material or a cyclic olefin copolymer (COC) material; a colour
filter substrate; a colour filter layer; an internal reactive
mesogen (RM) retarder alignment layer; an internal reactive mesogen
(RM) retarder; a liquid crystal (LC) layer; and a second linear
polarizer. The external retarder and the internal RM retarder are
configured such that optical properties (for example light
polarization control function) of the external retarder and the
internal retarder are matched to negate each other for light
passing through the external retarder and the internal RM retarder,
thereby simultaneously minimizing said unwanted internal ambient
light reflections and maintaining high contrast ratio for displayed
images.
[0025] FIG. 2 is a schematic drawing of an exemplary LCD optical
stack arrangement 101 in accordance with embodiments of the present
invention.
[0026] Referring to FIG. 2, an FFS or IPS type LCD 101 is
configured in a manner that significantly suppresses unwanted
internal reflections is described. Some components are comparable
as in the conventional configuration of FIG. 1, so like components
are identified with like reference numerals. From the viewing side,
the FFS or IPS type LCD 101 includes the anti-reflection film 13,
the CF substrate linear polariser 12, an external retarder 11, the
colour filter (CF) substrate 10, the colour filter layer 9, an
internal reactive mesogen (RM) retarder alignment layer 8, an
internal reactive mesogen (RM) retarder layer 7, the LC alignment
layer 6, the LC layer 5, the LC alignment layer 4, the active
matrix electrode layer 3, the TFT substrate 2, the TFT linear
polariser 1, and the backlight unit 300. All components, excluding
the backlight unit 300, described in the FFS or IPS type LCD 101
may be adhered together to prevent the formation of air gaps. All
retarders described herein are optical retarders that may change
the polarisation state of light. Accordingly, comparing FIG. 2 to
FIG. 1, the LCD 101 includes the following additional layers that
are not included in the conventional LCD 100: the external retarder
11, the internal RM retarder alignment layer 8, and the internal RM
retarder 7.
[0027] The alignment direction of the internal reactive mesogen
(RM) retarder alignment layer 8 may be formed via a rubbing process
or a UV photo-alignment process. If a UV photo-alignment process is
used, 254 nm UV radiation may be used (bond-breaking
photo-alignment) or 365 nm UV radiation may be used (bond-making
photo-alignment). The alignment direction of the internal reactive
mesogen (RM) retarder alignment layer 8 defines the alignment
direction of the optical axis of the internal reactive mesogen RM
retarder layer 7.
[0028] To ensure that the FFS or IPS type LCD 101 shown in FIG. 2
has the same dark room (i.e. in the absence of ambient lighting)
image quality as the FFS or IPS type LCD 100 shown in FIG. 1, the
external optical retarder 11 and the internal RM retarder layer 7
are configured so that their optical properties are matched to
negate each other for light passing through the external retarder
and the internal RM retarder. The external retarder 11 and the
internal RM retarder layer 7 in particular are configured such that
their polarisation control functions are matched to negate each
other. For example, if light that originates from the backlight has
its polarisation state modified from a linearly polarised state to
a left-handed circularly polarised state by the internal RM
retarder layer 7, then the external optical retarder 11 will
convert said left-handed circularly polarised state back to said
linearly polarised state. Also for example, if light that
originates from an ambient light source (e.g., sunshine or other
external light) has its polarisation state modified from a linearly
polarised state to a left-handed circularly polarised state by the
external optical retarder 11, then the internal RM retarder layer 7
will convert said left-handed circularly polarised state back to
said linearly polarised state. More generally, the effect of the
retarder layers 7 and 11 will then be for each to rotate the major
axis of the polarisation ellipse and alter the ellipticity, but
oppositely in each case, so when considered in combination, the
retarder layers 7 and 11 do not change the polarisation state of
the light that passes from the backlight 300 to the linear
polariser 12.
[0029] Referring to FIG. 2, the external retarder 11 is a laminated
film, and particularly may be configured as a quarter wave plate
(QWP or .lamda./4) film. The external retarder 11 is a positive
uniaxial material. In other words, the external retarder 11 is a
positive A-plate, and is orientated at substantially 45.degree.
(.+-.10.degree.) to the CF linear polariser 12. Ambient light from
the viewing side becomes circularly polarised after traversing the
combination of the CF linear polariser 12 and external retarder 11.
Reflection of circularly polarised light from components below,
i.e. further from the viewing side relative to the external
retarder 11, will be absorbed by the CF linear polariser 12, and
thus unwanted internal reflections are significantly reduced. The
external retarder 11 and the CF linear polariser 12 may be
fabricated as a composite film that forms a resultant circular
polariser.
[0030] The external retarder 11 is fabricated from a Cyclo Olefin
Polymer (COP) material or a Cyclo Olefin Copolymer (COC) material.
An advantage of the COP or COC material is that the retardation
versus wavelength is a relatively flat functional form for all
optical wavelengths (red, green and blue). COP and COC materials
have a relatively flat dispersion curve. A flat dispersion curve
enables the combination of the external retarder 11 and CF linear
polariser 12 to produce circularly polarised light across the
visible spectrum, and therefore significantly reduce internal
reflections in the manner described above. Another advantage of the
COP or COC material is that the COP or COC materials are found by
the inventors to be robust to the external environmental
conditions. Accordingly, the optical properties of the external
optical retarder 11 remain unaffected by high ambient lighting
conditions, large ambient temperature variations and large ambient
humidity variations. Consequently, regardless of the environmental
conditions, the external optical retarder 11 and CF linear
polariser 12 produce high quality circularly polarised light across
the visible spectrum, and therefore significantly reduce internal
reflections. The use of COP or COC material achieves unexpected and
enhanced results as compared to conventional configurations, in
that one can formulate an RM material with the same dispersion
characteristics as the COP or COC material, such that the external
optical retarder 11 and the internal RM retarder layer 7 have
optical functions that negate each other. Example COP or COC
materials that may be used in the present invention include
comparable materials as used in products such as, for example,
NZF-UF01A (Nitto Denko), ZeonorFilm.RTM. (Zeon Corporation) and
Arton Film.RTM. (JSR).
[0031] The internal RM retarder layer 7 may be coated onto the
internal RM retarder alignment layer 8. The RM coating method may
be a slot-die coating method or a spin coating method as are used
in the art. The internal RM retarder layer 7 may be configured as a
quarter wave plate (QWP or .lamda./4) film, and is a positive
uniaxial material. The internal RM retarder layer 7 thus is a
positive A-plate. The internal RM retarder layer is orientated at
substantially 90.degree. (.+-.10.degree.) to the external optical
retarder 11. An advantage of using an RM material for the internal
RM retarder layer 7 is that the thickness required to achieve a QWP
function can be sufficiently thin to minimise colour artefacts that
degrade the dark room image quality. Comparably as above,
unexpected and enhanced results are achieved by using an RM
material for the internal RM retarder layer 7, in that one can
formulate an RM material with the same dispersion characteristics
as the COP or COC material, such that the external optical retarder
11 and the internal RM retarder layer 7 have optical functions that
negate each other. The internal RM retarder layer 7 may have a
thickness less than 3.0 .mu.m, and particularly may have a
thickness less than 1.0 .mu.m.
[0032] To operate as described, with minimal impact on the
dark-room transmissive display quality, and in particular contrast
ratio, the laminated quarter wave plate external retarder 11 and
the internal RM quarter wave plate retarder 7 should operate to
effectively cancel as completely as possible each other's
polarisation control function for all wavelengths transmitted by
the LCD. It is an unexpected and enhanced result that the RM
material may be formulated so that after all manufacturing
processes are complete, the dispersion of the of the internal RM
quarter wave plate retarder 7 closely matches that of the
dispersion of the external laminated quarter wave plate retarder
11, and thus ensures a display with high image quality because
dark-room contrast ratio is high and reflections from ambient light
sources are low. Therefore, matching the optical properties, in
particular the polarization function of the external laminated
quarter wave plate retarder 11 and the internal reactive mesogen
quarter wave plate retarder 7, represents a solution with
unexpected and enhanced results in terms of optical performance,
high durability and relatively low cost.
[0033] The internal RM retarder layer 7 and the external retarder
layer 11 may have retardation values in the range 110 nm to 165 nm
measured at 550 nm. In a preferred embodiment, the internal RM
retarder layer 7 and the external retarder layer 11 may have
retardation values in the range 130 nm to 145 nm measured at 550
nm. The difference in retardation values measured at 550 nm between
the internal RM retarder layer 7 and the external retarder layer 11
may be approximately 0 nm to 10 nm, and preferably less than 5 nm.
In general, a smaller difference in retardation at a given
wavelength for the internal RM retarder layer 7 and the external
retarder layer 11 enables a displayed image with higher contrast
ratio. Therefore, a smaller difference in retardation at a given
wavelength for the internal RM retarder layer 7 and the external
retarder layer 11 is preferable. In general, a smaller difference
in retardation for the internal RM retarder layer 7 and the
external retarder layer 11 for all optical wavelengths is
preferable.
[0034] It may be difficult to maintain the same retardation
difference for the internal RM retarder layer 7 and the external
retarder layer 11 for each optical wavelength. Therefore, it may be
preferable to minimize the retardation difference for the internal
RM retarder layer 7 and the external retarder layer 11 for short
optical wavelengths (i.e. the blue part of the visible spectrum).
Alternatively, it may be preferable to minimize the retardation
difference for the internal RM retarder layer 7 and the external
retarder layer 11 for mid optical wavelengths (i.e. the green part
of the visible spectrum). Alternatively, it may be preferable to
minimise the retardation difference for the internal RM retarder
layer 7 and the external retarder layer 11 for long optical
wavelengths (i.e. the red part of the visible spectrum).
[0035] For the following discussion, let "R650" denote the
retardation of red light measured at 650 nm, "R550" denote the
retardation of green light measured at 550 nm, and "R450" denote
the retardation of blue light measured at 450 nm. It has been shown
that an LCD device has acceptable image quality in terms of
contrast ratio when the internal reactive mesogen quarter wave
plate retarder 7 has the value of R450/R550 in the range of 0.95 to
1.07 (1.01.+-.0.06), and the value of R650/R550 in the range of
0.93 to 1.05 (0.99.+-.0.06). Further enhanced image quality has
been shown for an LCD device in terms of contrast ratio when the
internal reactive mesogen quarter wave plate retarder 7 has the
value of R450/R550 in the range of 0.97 to 1.05 (1.01.+-.0.04), and
the value of R650/R550 in the range of 0.95 to 1.03 (0.99.+-.0.04).
Even further enhanced image quality has been shown for an LCD
device in terms of contrast ratio when the internal reactive
mesogen quarter wave plate internal retarder 7 has the value of
R450/R550 in the range of 0.99 to 1.03 (1.01.+-.0.02), and the
value of R650/R550 in the range of 0.97 to 1.01 0.99.+-.0.02.
[0036] In addition, it has been shown that an LCD device has
acceptable image quality in terms of contrast ratio when the
external laminated quarter wave plate retarder 11 has the value of
R450/R550 in the range of 0.95 to 1.07 (1.01.+-.0.06), and the
value of R650/R550 in the range 0.93 to 1.05 (0.99.+-.0.06).
Further enhanced image quality has been shown for an LCD device in
terms of contrast ratio when the external laminated quarter wave
plate retarder 11 has the value of R450/R550 in the range of 0.97
to 1.05 (1.01.+-.0.04), and the value of R650/R550 in the range
0.95 to 1.03 (0.99.+-.0.04). Even further enhanced image quality
has been shown for an LCD device in terms of contrast ratio when
the external laminated quarter wave plate retarder 11 has the value
of R450/R550 in the range of 0.99 to 1.03 (1.01.+-.0.02), and the
value of R650/R550 in the range of 0.97 to 1.01 (0.99.+-.0.02).
[0037] In addition, it has been shown that the LCD device has
acceptable image quality in terms of contrast ratio when both the
internal reactive mesogen quarter wave plate retarder 7 and
external laminated quarter wave plate retarder 11 have values of
R450/R550 in the range of 0.95 to 1.07 (1.01.+-.0.06), and values
of R650/R550 in the range of 0.93 to 1.05 (0.99.+-.0.06). Further
enhanced image quality has been shown for an LCD device in terms of
contrast ratio when both the internal reactive mesogen quarter wave
plate retarder 7 and external laminated quarter wave plate retarder
11 have values R450/R550 in the range of 0.97 to 1.05
(1.01.+-.0.04), and values of R650/R550 in the range of 0.95 to
1.03 (0.99.+-.0.04). Even further enhanced image quality has been
shown for an LCD device in terms of contrast ratio when both the
internal reactive mesogen quarter wave plate retarder 7 and
external laminated quarter wave plate retarder 11 have values
R450/R550 in the range of 0.99 to 1.03 (1.01.+-.0.02), and values
of R650/R550 in the range of 0.97 to 1.01 (0.99.+-.0.02).
Configurations of broader tolerance ranges tend to be easier to
manufacture, but have lower image contrast ratio. Conversely,
configurations with a narrower tolerance range tend to be harder to
manufacture, but have higher image contrast ratio. A broader
tolerance range also has more flexibility on design of RM material
chemistry.
[0038] An advantage of an external laminated quarter wave plate
retarder 11 is that circular polariser films comprised of a linear
polariser 12 plus a laminated quarter wave plate 11 are relatively
inexpensive and durable. Environmental durability is significant
for the external quarter wave plate 11. In addition, an advantage
of an internal reactive mesogen quarter wave plate retarder 7 is
that such a retarder is considerably thinner than the external
laminated quarter wave plate 11, and therefore the internal
reactive mesogen quarter wave plate retarder 7 will not have a
detrimental effect on the liquid crystal cell gap. A further
advantage of using a relatively thin internal reactive mesogen
quarter wave plate retarder 7 is the avoidance of colour artefacts.
Colour artefacts occur when light from a first pixel region passes
through the colour filter of a second pixel, whereby the first and
second pixel regions are of the same or different colours. This
type of colour artefact is minimised by minimising the thickness of
the reactive mesogen quarter wave plate retarder 7. Accordingly, a
combination of an external laminated quarter wave plate retarder 11
and an internal reactive mesogen quarter wave plate retarder 7
represents a solution with unexpected and enhanced results in terms
of optical performance, durability and low cost.
[0039] FIG. 3 is a drawing that defines the azimuthal orientation
directions in an LCD device configured as described, and FIG. 4 is
a chart that defines the azimuthal orientation directions of some
of the optical components. Referring to FIG. 3, a plan view of the
FFS or IPS type LCD 101 is shown with azimuth orientation angle,
.phi., shown. Referring to FIG. 4, a table of components within the
FFS or IPS type LCD 101 is shown along with azimuthal orientation
angles for the respective components, which include: transmission
axis of TFT substrate linear polariser 1, alignment direction of
TFT substrate LC alignment layer 4, alignment direction of CF
substrate LC alignment layer 6, optical axis of internal RM
retarder layer 7, optical axis of external laminated retarder 11
and transmission axis of CF substrate linear polariser 12. The
azimuthal orientation direction of the internal RM retarder
alignment layer 8 and optical axis of internal RM retarder layer 7
are always the same.
[0040] Although precise values are shown for all azimuthal
orientation angles (.phi.) in FIG. 4, it will be appreciated that
manufacturing tolerances and related processing can limit the
accuracy that can be obtained. Therefore, the azimuthal orientation
angles (.phi.) referred to in FIG. 4 are aspirational for optimum
performance. Referring to FIG. 4, the value of x.degree. may take
any value between 0.degree. and 36.degree., and most commonly has a
value of 0.degree. or 90.degree.. Components such as the linear
polarisers 1, 12 and the retarders 7, 11 have symmetry such that
alignment directions of .phi. and .phi.+180.degree. are equivalent.
Also referring to FIG. 4, the value of "n" may take the values 1,
3, 5, 7 etc. The difference in azimuthal orientation angle of the
alignment direction of TFT substrate LC alignment layer 4 and the
alignment direction of CF substrate LC alignment layer 6 is always
180.degree. for a non-zero LC pretilt angle. In other words, the LC
alignment is anti-parallel for LCs with a non-zero pretilt. If the
LC has no pretilt angle, then the difference between the alignment
direction of CF substrate LC alignment layer 6 and the alignment
direction of TFT substrate LC alignment layer 4 may be 0.degree. or
180.degree..
[0041] The difference in azimuthal orientation angle of the
transmission axis of CF substrate linear polariser 12 and optical
axis of external laminated retarder 11 is 45.degree., such that the
CF substrate linear polariser 12 and the optical axis of external
laminated retarder 11 form a circular polariser. The difference in
azimuthal orientation angle of the optical axis of external
laminated retarder 11 and the optical axis of internal RM retarder
layer 7 is 90.degree., i.e. the polarisation functions of the
external laminated retarder 11 and the internal RM retarder layer 7
cancel each other for light transmitted through both retarders 7,
11. The difference in azimuthal orientation angle of the
transmission axis of CF substrate linear polariser 12 and
transmission axis of TFT substrate linear polariser 1 is
90.degree., i.e. the linear polarisers 1 and 12 are crossed. Unless
stated otherwise, the azimuthal orientation angles of the
components shown in FIG. 4 apply to all subsequent embodiments.
[0042] FIG. 5 is a schematic drawing of another LCD optical stack
arrangement in accordance with embodiments of the present
invention. FIG. 5 depicts an FFS or IPS type LCD 102 that also
significantly suppresses unwanted internal reflections, and has
additional components that further improve image quality.
Accordingly, components in common with previous embodiments are
identified with like reference numerals, with the additional
components identified in FIG. 5. The FFS or IPS type LCD 102
further includes an electromagnetic shielding layer 91 that may be
deposited onto the CF substrate 10 and is positioned between the
colour filter substrate 10 and the colour filter layer 9. The
electromagnetic shielding layer 91 is a conductive layer and may be
an ITO layer.
[0043] The FFS or IPS type LCD 102 further includes a first
planarization layer 81 that may be deposited on a non-viewing side
of the colour filter layer 9 and is used to eliminate surface
roughness of the colour filter layer 9. It is desirable that the
planarization layer 81 be as thin as possible to avoid colour
artefacts. The thickest part of the planarization layer 81 may be
less than 5 .mu.m, and in exemplary embodiments is less than 2
.mu.m.
[0044] The FFS or IPS type LCD 102 further includes a second
planarization layer 62 that may be deposited on a non-viewing side
of the internal RM retarder layer 7 and is used to eliminate
surface roughness of the internal RM retarder layer 7. It is
desirable that the second planarization layer 62 also be as thin as
possible to avoid colour artefacts. The thickest part of the
planarization layer 62 may be less than 2 .mu.m, and more
preferably the thickest part of the planarization layer 62 may be
less than 1 .mu.m.
[0045] The FFS or IPS type LCD 102 further includes a photospacer
layer 61 that may be deposited on the non-viewing side of the
internal RM retarder 7. For example, the photospacer layer 61 may
be deposited on the second planarisation layer 62 as shown in FIG.
5. If a second planarisation layer 62 is not used, then the
photospacer layer 61 may be deposited directly on the internal RM
layer 7. The purpose of the photospacer layer 61 is to maintain a
uniform thickness of the LC layer 5.
[0046] FIG. 6 is a schematic drawing of another LCD optical stack
arrangement in accordance with embodiments of the present
invention. The FFS or IPS type LCD 103 is a modification to the FFS
or IPS type LCD 102 and includes a positive uniaxial retarder 95
with optical axis orientated in the viewing direction (i.e., a
positive C-plate retarder) that may be positioned between the
external retarder 11 and internal RM retarder 7. In other words, at
least a first positive C-plate retarder 95 may be positioned
between the external retarder 11 and internal RM retarder 7.
Although FIG. 6 shows all the possible locations for the positive
C-plate retarder 95, the positive C-plate retarder 95 may take at
least one of the positions as shown in FIG. 6. For example,
positive uniaxial retarder 95 may just be located between the
external retarder 11 and CF Substrate 10.
[0047] The purpose of the positive C-plate retarder is to
compensate for the off-axis viewing degradation that can occur due
to the combination of the external retarder 11 and internal RM
retarder 7. The positive C-plate retarder may have a retardation
value in the range of 80 nm-200 nm. The optimal positive
retardation value for the positive C-plate retarder may depend on
the biaxiality of external retarder 11. The positive C-plate
retarder may be a film laminated to the exterior of the FFS or IPS
type LCD 102, for example, between the external retarder 11 and the
CF substrate 10. The positive C-plate retarder may be part of a
composite film that also contains the external retarder 11. The
positive C-plate retarder may be part of a composite laminated film
that also contains the external retarder 11 and the linear
polariser 12. The positive C-plate retarder may be an RM layer
disposed on the interior of the FFS or IPS type LCD 102, positioned
between the internal RM retarder 7 and the colour filter substrate
10. If the positive C-plate retarder is an RM layer, then an
appropriate alignment layer (not shown) may be required. The
alignment layer for the RM positive C-plate retarder layer may
promote vertical alignment of the RM molecules.
[0048] In the embodiments of FIG. 5 and FIG. 6, a number of
additional uniaxial or biaxial retardation films (not shown) may be
positioned between the TFT substrate linear polariser 1 and the CF
substrate linear polariser 12 to compensate the off-axis viewing
degradation that can occur due to the LC layer 5 and/or the
combination of the CF substrate linear polariser and the TFT
substrate linear polarizer.
[0049] An aspect of the invention, therefore, is a liquid crystal
device (LCD) that is configured for minimizing unwanted ambient
light reflections particularly from internal components. In
exemplary embodiments, the LCD includes a plurality of layers, the
layers comprising from a viewing side: a first linear polariser; an
external retarder that is made of a cyclic olefin polymer (COP)
material or a cyclic olefin copolymer (COC) material; a colour
filter substrate; a colour filter layer; an internal reactive
mesogen (RM) retarder alignment layer; an internal reactive mesogen
(RM) retarder; a liquid crystal (LC) layer; and a second linear
polarizer. The LCD may include one or more of the following
features, either individually or in combination.
[0050] In an exemplary embodiment of the LCD, the external retarder
and the internal RM retarder are configured such that optical
properties of the external retarder and the internal RM retarder
are matched to negate each other for light passing through the
external retarder and the internal RM retarder.
[0051] In an exemplary embodiment of the LCD, the matched optical
properties include light polarization control function.
[0052] In an exemplary embodiment of the LCD, an azimuthal angle
between the first and second linear polarisers is 90.degree., an
azimuthal angle between the first linear polariser and the external
retarder is 45.degree., and an azimuthal angle between the internal
RM retarder and external retarder is 90.degree..
[0053] In an exemplary embodiment of the LCD, the internal RM
retarder is made of a positive uniaxial material.
[0054] In an exemplary embodiment of the LCD, the external retarder
is made of a positive uniaxial material.
[0055] In an exemplary embodiment of the LCD, the external retarder
is a laminated film that is configured as a quarter wave plate.
[0056] In an exemplary embodiment of the LCD, the internal RM
retarder is a film that is configured as a quarter wave plate.
[0057] In an exemplary embodiment of the LCD, the internal RM
retarder and the external retarder layer each has a retardation
value in a range of 110 nm to 165 nm measured at 550 nm.
[0058] In an exemplary embodiment of the LCD, a difference in
retardation values measured at 550 nm between the internal RM
retarder layer and the external retarder layer is in a range of 0
nm to 10 nm.
[0059] In an exemplary embodiment of the LCD, R450 denotes
retardation of blue light measured at 450 nm, R550 denotes
retardation of green light measured at 550 nm, and R650 denotes
retardation of red light at 650 nm; and the internal RM retarder
layer has a value of R450/R550 in a range of 0.95 to 1.07
(1.01.+-.0.06), and a value of R650/R550 in a range of 0.93 to 1.05
(0.99.+-.0.06).
[0060] In an exemplary embodiment of the LCD, R450 denotes
retardation of blue light measured at 450 nm, R550 denotes
retardation of green light measured at 550 nm, and R650 denotes
retardation of red light at 650 nm; and the external retarder has a
value of R450/R550 in a range of 0.95 to 1.07 (1.01.+-.0.06), and a
value of R650/R550 in the range of 0.93 to 1.05 (0.99.+-.0.06).
[0061] In an exemplary embodiment of the LCD, the LCD further
includes an electromagnetic shielding layer that is deposited onto
the color filter substrate and is positioned between the colour
filter substrate and the colour filter layer. In an exemplary
embodiment of the LCD, the electromagnetic shielding layer is a
conductive layer.
[0062] In an exemplary embodiment of the LCD, the LCD further
includes a first planarization layer deposited on a non-viewing
side of the colour filter layer that eliminates surface roughness
of the colour filter layer.
[0063] In an exemplary embodiment of the LCD, the LCD further
includes a second planarization layer deposited on the non-viewing
side of the internal RM retarder that eliminates surface roughness
of the internal RM retarder.
[0064] In an exemplary embodiment of the LCD, the LCD further
includes a photospacer layer deposited on a non-viewing side of the
internal RM retarder that is configured to maintain uniform
thickness of the LC layer.
[0065] In an exemplary embodiment of the LCD, the LCD further
includes an anti-reflection film located on the viewing side of the
first linear polarizer.
[0066] In an exemplary embodiment of the LCD, the LCD further
includes at least a one C-plate retarder deposited between the
external retarder and internal RM retarder.
[0067] Although the invention has been shown and described with
respect to a certain embodiment or embodiments, it is obvious that
equivalent alterations and modifications will occur to others
skilled in the art upon the reading and understanding of this
specification and the annexed drawings. In particular regard to the
various functions performed by the above described elements
(components, assemblies, devices, compositions, etc.), the terms
(including a reference to a "means") used to describe such elements
are intended to correspond, unless otherwise indicated, to any
element which performs the specified function of the described
element (i.e., that is functionally equivalent), even though not
structurally equivalent to the disclosed structure which performs
the function in the herein illustrated exemplary embodiment or
embodiments of the invention. In addition, while a particular
feature of the invention may have been described above with respect
to only one or more of several illustrated embodiments, such
feature may be combined with one or more other features of the
other embodiments, as may be desired and advantageous for any given
or particular application.
INDUSTRIAL APPLICABILITY
[0068] Embodiments of the present invention are applicable to many
display devices, and a user may benefit from the capability of the
display to provide improved display visibility under higher ambient
illumination, without the need for increased backlight power,
particularly when the display is battery powered. Examples of such
devices include mobile phones, personal digital assistants (PDAs),
tablet and laptop computers, desktop monitors, and digital
cameras.
REFERENCE SIGNS LIST
[0069] 1 TFT Linear Polariser
[0070] 2 TFT Substrate
[0071] 3 Active Matrix Electrodes
[0072] 4 First LC Alignment layer
[0073] 5 LC
[0074] 6 Second LC Alignment Layer
[0075] 7 Internal RM Retarder
[0076] 8 Internal RM Retarder Alignment Layer
[0077] 9 Colour Filter (CF) Layer
[0078] 10 CF Substrate
[0079] 11 External Retarder .lamda./4
[0080] 12 CF Substrate Linear Polariser
[0081] 13 Anti-reflection Film
[0082] 61 Photospacer Layer
[0083] 62 Second Planarization Layer
[0084] 81 First Planarization Layer
[0085] 91 Electromagnetic Interference Shielding
[0086] 95 C-plate retarder
[0087] 100 Conventional FFS or IPS Type LCD
[0088] 101 FFS or IPS type LCD With External and Internal
Retarders
[0089] 102 Another FFS or IPS type LCD With External and Internal
Retarders
[0090] 103 Yet another FFS or IPS type LCD With External and
Internal Retarders
[0091] 200 Viewing Side
[0092] 300 Backlight Unit
* * * * *